A. Field of Invention
This invention pertains to talk-through units, and more particularly to a talk through unit in which speech is automatically muted at least in one direction, and restored in response to voice signals in the opposite direction.
B. Description of the Prior Art
In many instances it is desirable to provide a two-way communication system for bridging a partition. For example, many ticket booths used for dispensing tickets at train stations, theaters, sporting arenas and so forth are provided with bullet proof windows for the protection of the attendant. Communication between a potential customer and the attendant is provided by a two way talk unit, such as as described in commonly assigned U.S. Pat. No. 4,049,911, incorporated herein by reference. The unit described in this reference, is preferably mounted on the window partition and includes two sets of speakers and microphones. An external microphone is used to pick up sounds from the customer and transmit them to an internal speaker. An internal microphone, preferably disposed on a flexible extension, referred to as the "goose-neck", transmits the sounds from the attendant to an external speaker. Control circuitry is provided to selectively amplify the sounds in both directions. More specifically, sounds from inside the booth are not picked up and transmitted unless the attendant speaks within a short distance, i.e., two inches, from the internal microphone. External sounds are compressed so that they are reproduced at a preselected constant maximum amplitude.
A problem with this system is that sudden loud background external noises, such as generated for example by a large crowd at a sports arena, or by a train in a train station, are propagated indiscriminately into the booth, and can be discomforting to the attendant, especially over long time periods.
Other two way communication systems are known in the art. For example, U.S. Pat. No. 3,291,911 discloses a system wherein one of the two way channels is partially muted when not in use. The channel automatically turns off its own muting when it receives an input signal. U.S. Pat. No. 4,588,859 a two channel system is disclosed wherein each channel mutes the other channel when receiving an input signal.
Japanese Patent 63-48937 discloses a muting circuit in a telephone system with a predetermined time delay.
The following references also disclose other communication schemes: 3215780; 3999015; 43084278; 4319086; 4691348.
None of these schemes solve the abovementioned problems satisfactorily.